Phthorimaea operculella Zeller

Phthorimaea operculella attacks stems, leaves and tubers. It is a native of South America where it is associated with a rich parasitoid complex. P. operculella was introduced into India from Italy along with seed potatoes in 1906. By now it has become the most destructive pest of potato in Karnataka and Maharashtra. It also causes damage in south Bihar hills, south Madhya Pradesh, pockets of Meghalaya, Tamil Nadu and Himachal Pradesh and has spread to many new potato growing areas of the country. It initially acts as leaf-miner and later as a tuber borer. It is known to cause severe damage rendering the tubers unfit for human consumption. In country stores (where potatoes are generally stored for future consumption or seed purposes), the female deposits its eggs on the eyes of the tubers, 58 to 168 eggs are laid by each female in 4 to 5 days of its lifetime. The eggs hatch in 2-3 days and the larvae bore into potato tubers where they feed extensively. In each tuber 3 to 19 larvae are found. The larvae complete feeding in 7 to 9 days and come out of the tuber. The larvae turn into pupae by selecting a suitable substrate for pupation. It may be a piece of gunny bag with which the baskets are lined on in sand on which potatoes are generally kept. The pupae are formed within 2 days and the adult emerges from these pupae in 4 to 7 days. The life cycle is completed in 14-22 days. The pest can complete 10-13 generations in a year. P. operculella is used as a host for producing many natural enemies.

For maintaining the host culture a cabinet is constructed. It is a compact unit with 15 wire-mesh trays which rest on aluminium channels and in which infested tubers are placed. Two plywood planks are provided at the bottom, over which a thin layer of sterile sand is spread to enable larvae to pupate. Freshly infested tubers are placed in the lower trays with the oldest in the bottom-most tray. Tubers are infested in the cabinet itself by spreading an egg bearing cloth over fresh tubers which have been perforated. This is done by rolling the potatoes over a board with nails driven through it (100 nails measuring 1.25 cm in length are fitted in an area of 7x7 cm on a piece of wood measuring 30xl0 cm). The cloth is removed and potatoes spread out after the eggs have hatched. Within 2 weeks the larvae complete feeding, emerge from the tubers and pupate in the sand, kept at the bottom. The cocoons are then scraped off from the plywood plank on alternate days. On the 15th day, tubers from which the larvae have emerged are removed from the cabinet and kept in a separate cage (30 cm3) for adult emergence (as more than 10% of the larvae pupate within the tubers).

Moths that emerge are collected into an egg laying cage which is prepared by converting an ordinary plastic bread box (24 x 12.5 x 10 cm). A 2.5 cm hole is cut on the side wall of the bread box for the introduction of moths and 2 cotton swabs dipped in 50% honey are kept inside for adult feeding. A double layer of muslin is spread over the mouth of the bread box and covered over by the lid, the central portion of which has been cut out. The complete unit is then secured with rubber bands. Eggs are laid by the moths between the two layers of cloth.

It has been determined that one kg of potato tubers is sufficient for development of larvae hatching from 2000 eggs and of these, on an average 76% pupate successfully.